The aim of this investigation is to study the role of cell surface glycoproteins in embryonic development. Studies will be carried out using developing sea urchin embryos, as well as cultured cells isolated from embryos. Using embryos, it has been established that tunicamycin, a specific inhibitor of the assembly of lipid-linked oligosaccharide precursors of N-glycosidically-linked glycoproteins, inhibits gastrulation without having any effect on earlier embryonic development. These results suggest that synthesis of certain N-glycosidically linked glycoproteins in essential for some step in the cellular rearrangements and migratins that occur during gastrulation. To determine which glyco-proteins are required in gastrulation, the labeled glycoproteins of embryos undergoing gastrulation will be characterized and compared with those in tunicamycin-inhibited cells. Using labeled antibodies it may be possible to define the specific cell type that synthesizes these glycoproteins. This approach, using a specific inhibitor, will be complemented by similar studies carried out using a pair of interspecies hybrid embryos, one which undergoes normal gastrulation, whereas the other does not. To gain an understanding of the relationship between biosynthesis of N-glycosidically linked glycoproteins and cell differentiation, micromeres, which are destined to become mesodermal cells that give rise to primary mesenchymal cells, will be isolated from 16-cell stage embryos and cultured in vitro. In addition primary mesenchymal cells will be isolated from embryos and cultured. Changes in glycoprotein synthesis, and in the lipid-linked oligosaccharides involved in glycoprotein synthesis, will be studied throughout the course of differentiation of these cells to spicule-forming aggregates.